Made mistake by using personal email: Carter

US Defence Secretary Ashton Carter has admitted he made a mistake by using his personal email for official work as the opposition Republican party used this as an opportunity for slamming the Obama Administration.

"This is a mistake I made with respect to e-mail; entirely my mistake; entirely on me," Carter told reporters travelling with him in Erbil, Iraq after it emerged that he used his personal email for government business in the early part of his tenure, triggering concerns hackers could access sensitive information.

He said as Secretary of Defence, he does use e-mail very much.

"I certainly don't use it for classified information, and any work-related e-mail is preserved, as is required," he noted.

"But what I was doing that I shouldn't have been doing, until a few months ago, which meant I was doing it longer than I should have been, obviously -- is using my iPhone, which has my personal e-mail on it, to send messages to my office -- administrative messages; not classified information.

"And all of this is preserved as a public record as it should be," Carter said.

"But that I shouldn't have been doing. And I've stopped doing that, but that was a mistake. And to get to your question, I mean, particularly someone in my position and the sensitivities about the position should have known better," he added.

Senator John McCain, Chairman of the Senate Armed Services Committee, said with all the public attention surrounding the improper use of personal email by other Administration officials, it is hard to believe that Carter would exercise the same error in judgement.

"The Senate Armed Services Committee has requested copies of the emails and will be conducting a review to ensure that sensitive information was not compromised," he said.

Both the White House and the Pentagon said they prepared to cooperate with legitimate congressional oversight into this matter.

"Carter also indicated, finally, that he has curtailed his use of any email whatsoever, but certainly will ensure, moving forward, that emails about his government work is conducted on his government email consistent with administration policy," White House Press Secretary Josh Earnest told reporters at his daily news conference.

According to Earnest, the White House Chief of Staff did ask the Counsel's Office here at the White House to contact senior officials at the Pentagon to alert them to concerns about email use, and those concerns were relayed.

"As Secretary Carter himself admitted, he did make that same mistake. I think it's obviously a mistake, but to his credit, he owned up to it. He took full responsibility for it. And most importantly, actually, he's taken the steps that are necessary to rectify it," Earnest said.

Earlier, Hillary Clinton came under fire for using her personal email account for conducing official business, including communications with the foreign leaders and diplomats, when she worked as the US Secretary of State.